The propene molecule C3H6, aka propylene, has been identified in spectra recorded toward TMC-1 by
N. Marcelino, J. Cernicharo, M. Agúndez, E. Roueff, M. Gerin, J. Martín-Pintado, R. Mauersberger, and C. Thum,
Discovery of Interstellar Propylene (CH<sub>2</sub>CHCH<sub>3</sub>): Missing Links in Interstellar Gas-Phase Chemistry
Astrophys. J. 665, L127–L130 (2007).
Six rotational transitions each split into two A and E components due to the CH3 interal rotation were observed plus one A component for which the E line is overlapped. The observation of this molecule in TMC-1 was rather surprising because apparently noone in the community considered such an almost saturated molecule to be likely in this source – especially because of thus far missing routes to this molecule. Even more remarkable is the detection because of the high abundance; a column density of 4 × 1013 cm-2 was derived; comparable to the abundance of c-C3H2.

M. Agúndez, J. Cernicharo, and M. Guélin
reported the detection of propene by the two methyl internal rotor states of the 505 – 404 transition near 86.65 GHz with the IRAM 30 m telescope toward 4 out of 5 dark clouds (Lupus-1a, L1495B, L1521F, and Serpens South 1a) in their report on
Discovery of Interstellar Ketenyl (HCCO), a Surprisingly Abundant Radical
Astron. Astrophys. 577, Art. No. L5 (2015).
Emission of up to three more rotational transitions were also detected.

S. Manigand, A. Coutens, J.-C. Loison, V. Wakelam, H. Calcutt, H. S. P. Müller, J. K. Jørgensen, V. Taquet, S. F. Wampfler, T. L. Bourke, B. M. Kulterer, E. F. van Dishoeck, M. N. Drozdovskaya, and N. F. W. Ligterink
reported on
The ALMA-PILS Survey: First Detection of the Unsaturated Three-carbon Molecules Propenal (C<sub>2</sub>H<sub>3</sub>CHO) and Propylene (C<sub>3</sub>H<sub>6</sub>) towards the Low-mass Protostar IRAS 16293–2422 B
Astron. Astrophys. 645, Art. No. A53 (2021).
This is the first account on luke-warm (~ 75 K) propene in the ISM and on the detection of propene around a low-mass protostar. The Protostellar Interferometric Line Survey (PILS) was carried out with ALMA in its Band 7 (329 – 363 GHz) with additional observations in Band 6. A total of 17 different unblended (with respect to a different molecule) lines were identified.

Contributor(s): H. S. P. Müller; 08, 2007; 05, 2015; 02, 2021

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